Peavey Classic 30 eating Preamp tubes.

[Shawnobi]

Put a fresh set of preamp tubes in the PV about early last year after they died halfway though a gig. This week V1 & V2 died together at rehearsal. I popped some fresh ones in and the amp sounds fine. But getting a year out of preamp tubes seems a little harsh to me. And both dying at once sounds suspect? Any thoughts from anyone? I want to takes some voltage readings this weekend, but as anyone familiar knows the C30 is a folded PCB design and is an absolute pig to work on.

[Enzo]

Let us define what you mean by "died."

Amps do not need tubes in sets. if you are talking about the tube heaters, they are wired in series, so if one opens they all go dark. Open tube heaters are exceedingly rare. If the heaters go out it is almost always something other than the tube itself.

I would bet that when your tubes died, if you had pulled the old tubes out and simply put them back in, that would have worked as well. It was the pushing and pulling on the tubes that made the amp work, not the newness of the tube.

I will wager my lunch money that you have failed solder on one or two of the bare wire jumpers between the circuit boards.

Look on the center board at the end near the fuses, there are two crosswise power resistors. They are in series with your preamp tube heaters. By the ends of those resistors are two bare wire jumpers to the other boards. Two to each other board. I bet the solder has cooked on one or more.

[Shawnobi]

Well I have a little valvecaster overdrive pedal which uses a 12AX7. I took the tubes out of the peavey and popped them into the pedal. Neither of the heaters lit up (from V1 or V2) which I guess points to the heater circuit being 'open' on both. So I figure I need to measure the 6.3V feed to FilA & B and see how that is looking.

Regarding those resistors near the fuses (R71 & R72, yes?) I have had a broken jumper there before which needed repair. On the plus side when I had that jumper issue last time I bought a bulk of those resistors in leiu of repair.

[Enzo]

Take it from me, burnt out heaters is extremely rare. But if you have it you have it. The only thing in an amp that would burnt out preamp tube heaters would be a short from the heater line to some high voltage line. That could be from an arc, or from a shorted power tube.

There is no 6.3v heater feed on a Classic 30.

Oh wow, I am very sorry. Those two crosswise resistors serve the power tube heaters, not the preamp heaters. You still may have jumper issues, but not specifically those. Sorry.

But your preamp tubes still don't use 6.3VAC. You have three small tubes, the two preamp tubes and the phase splitter of the power amp. They are all wired for 12v heayer operation and are in fact all three wired in series. They are connected then to the -36v power supply. So three 12v tubes in series across a 36v supply. R66 is the source of -36v.


And for notes: the four power tubes are wired in series across 24vAC.

[Shawnobi]

Take it from me, burnt out heaters is extremely rare. But if you have it you have it. The only thing in an amp that would burnt out preamp tube heaters would be a short from the heater line to some high voltage line. That could be from an arc, or from a shorted power tube.

There is no 6.3v heater feed on a Classic 30.

Oh wow, I am very sorry. Those two crosswise resistors serve the power tube heaters, not the preamp heaters. You still may have jumper issues, but not specifically those. Sorry.

But your preamp tubes still don't use 6.3VAC. You have three small tubes, the two preamp tubes and the phase splitter of the power amp. They are all wired for 12v heayer operation and are in fact all three wired in series. They are connected then to the -36v power supply. So three 12v tubes in series across a 36v supply. R66 is the source of -36v.


And for notes: the four power tubes are wired in series across 24vAC.

Well I think the valvecaster test may have been a red herring. Just put the original tubes back in and they work... The glow isn't as clear as the other 12ax7's I have. So maybe I was foiled by daylight. Thanks for giving me the motive to double-check. So I'm going to check for a loose jumper, now.